Signaling method and system



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R. V. L. HARTLEY SIGNALING METHOD AND SYSTEM Filed Dec. 31. 1920 2 Sheets-Shea*4 l R. V. L.. HARTLEY SIGNALING METHOD AND SYSTEM Filed Deo. 3l, 1920 2 Shets-Sheet 2 kut" ult@ Patented Nov. `16, 1926.

UNITED STATIESv Nla'rl.=:1\rr OFFICE. A

RALPH V. L.' HARTLEY,N(\)F EAST' ORANGE, NEW `JERSEY, .ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORVK, N. Y., A CORPORATION OF NEW YORK:

i SIGNALING METHOD AND SYSTEM.

Application filed December 31, 1920. Serial No. 484,192.

This invention relates to signaling systems and more particularly it relates to methods and systems for secret signaling.

' One of the object/s of this invention is to. provide a signaling method and system'by means vot' which signals such as telephone signals can be transmitted without any .danger of the signals being intelligently re-v ceived by persons vnot equipped with the special receiving apparatus of thisl invention. i

The preferred embodiment of this invention -by means of `which the above object is obtained employs two separate signaling channels and the signaling is obtained by switching 'the sending and receiving instruments synchronously from the channel to the other at irregular intervals in accordance with a code and at such a speed that the portions transmitted solely by each channel are unintelligible. If desired a source of meaningless signals can at the same time be switched so as to be always on the line which is not being used for the transmission of the true signals. Still further diiiiculty in deciphering the messages impressed upon the signaling channels can be obtained by having the intensity of the meaningless signals or noise vary in intensity with the true signals. y

-This invention will be better vunderstood by having reference to the following detailed' description taken in'connection with the accompanying drawings in which Figure 1 represents an' embodiment of thisinvention in which mechanical switching means are employed `for switching the source of sig'- nals from one signaling channel to another, Figure 2- represents in perspective the mechanical switching means employed in Figure 1 and Figure 3 represents an embodiment of this invention in which the switching from one signaling channel to another is accomplished by the intermediation il vacuum tubes. l

Referring to Figure 1 the signaling system disclosed therein comprises two lines and 11 which serve to inter-connect the combined transmitting and receiving stations 12 and 13. The station 12 comprisesan ordinary subscriber set including a transmitter 14 and a receiver 9. By a mechanical switching arrangement for alternately connecting contacts 21 and 22 to contacts 23` and 24, signals from the transmitter 14 are adapted. to be impressed at one time upon line 10 and at another time upon line 11. The same switching means also operates to associate the source of meaningless signals or noise with lines 10 and 11 in such a way that the noise currents are at any particular time impressed on that line which is not associated with the transmitter 14.

At any particular instant therefore, line 10 for example, will contain signaling currents, while line 11 -will contain noise currents; and at another instant, determined bythe mechanical switching means, line 11 willi contain the signaling currents and line 10 will contain the noise currents.

The switching arrangement by means of which the two lines 10 and 11 are alternately connected to the transmitter 14 and alternately Aconnected to a source of noise 15 is shown in detail in Figure 2 in which .16 represents an endless perforated tape which is adapted to travel over two rollers 17 andl 18., These two rollers have spaced pins-in their periphery which co-operate with slots in the tape 16 whereby the tape is adapted to be continuously moved by the motor 48;

19 is a block of conducting material which lby a lead 2O is adapted to be connected to`- p contact 23 of Figure 1. Positioned in the groove formed in block 19 and insulated therefrom is a second block for conducting material 26 which by a lead 27 is adapted to be connected to Contact 24 o'Figure 1. As'shown, tape 16 is adapted to pass over the uppei; surface of blocks 19 and 26 and 9 the tape 16 is provided with a plurality of slots 30, each of which when passing over blocks 26 and 19 allows a pin A31 to contact wwith block 19 and 'allows a pin 32 to contact line 10.

with block 26. These pins .31 and 32 by leads and 33 are adapted to be connected to contacts 21 and 22 respectively of Figure 1. Tape 16 also contains aplurality of slots 35. each of which when over blocks 19 and 26 allows pin 36 'to contact with block 26 and pin 37 to contact Withvblock 19. Pins 36l and 37 by leads 25 and 33 are adapted to be connected to contacts 21 and 22 respectively. Itis, therefore, evident that when a slot allows pins 31 and 32 to contact with blocks 19 land l26 respectively, contact 21 of Figure 1 will be connected to contact 23 and contact 22 will be connected .to contact 24. This will connect winding 40 of transformer 41 in series withV winding 42 of transformer 43'and will connect winding 44 of transformer 45 in series with winding 46 of transformer 47. With such an arrangement it is evident that signals from the transmitter 14 b transformers 41.4and 43 will be impresse on line 10 and noise currents `from source 15 by transformers' 45 and 47 will beimpressed on line 11. If on the other hand, a slot happens at a particular instantl to allow pins 36 and 37 to 'contact respectively with blocks 26 and 19, contact 21 will thenbe connected to contact 24 and contact 22 will be connected to contact 23. .This connects winding in series with winding 46 so that signals from 'the transmitter 1.4 are impressed on line 11 and connects winding 44 in series with winding 42 so that the noise rIfhe length of each slot 3() and 35 may be varied in any way desired to 'produce an irregular switching of the talking currents' from one line to the other. In some cases 1t may be found desirable to lhave two yslots 30 for example` follow eachother directly without the intervention of a slot 35 in pass-l ing from one of these two adjacent slots to the other. This will give rise to a small click in the outgoing line which however, will not indicate a switching4 of the signals from one line to the other. -These false.

clicks obtained will render still more diicult the intelligible detection 4of thesignals by any one notprovided with the special ref ceiving apparatus hereinafter described.

The diiiiculty ofv deciphering the message strength yof the telephone signals from trans? mitter 14. vAs shown in Fig. `1, transmitter 14 1s also connected by a transformer z50 to the input circuit of a vacuum .tube 51. The

output circuit of the tube 51 includes .4a.

source of voltage 49 in series with a resist"- ance 53 which is shunted by a path including a condenser 52. Resistance 53 is also in-v cluded between the control electrode '54 and the cathode of an amplifier 56..l The out# currents are` impressed on l' woef/ca put' circuit of tube 51 by a transformer 45 is adapted to be associated with the outgoing lines 10 and 11. Tube 51 and its ,associated apparatus should be so adjusted that for zero input potentials from source 14 substantially all of the electrons emitted by the cathode 48 of tube 51 pass to its anode. The effect of an alternating current voltage from source 14 can cause therefore only a decrease in the output current of tube 51 and the amount of the decrease will be proportional to the intenslty. of the currents 4from source 14. The shunt path including condenser 52 should have such an impedance as toV prevent currents of .speech frequencies from passing through the resistance 53, while still allowing the direct current passing through the resistance to decrease, each time a word is spoken in transmitter 14, an amount proportional to the intensity. of the currents produced thereby. Since resistance 53 has its negative end connected to control electrode 54 so that a decrease vin the I R drop in resistance 53 makes control electrodo 54 less negative, it follows that the value of the output current of tube 56 will be directly Aproportional `to the strength of the signals from source 14. The potential of control electrode 54 by a 'transformer 57 is also varied inl accordance with currents from the sourceof noise 15. 'Transformer 45 therefore is adapted to impress on the outgoing lines noise currents varying in intensity with the intensity of the signals from source 14. p If desired the I R drop through resistance 53 may be'made such that in the absence o f si als from source 14, the space current of tulble 56 is zero even for maximum positive values of the -voltages received from source 60. In such a case noise currents from source 15 will be impressed on th'e line only when transmitter 14 is actuated.'

The source of `noise currents may be of any suitable type, for example, it may be a telephone transmitter 60 which is associated Vwith a phonograph 61.. The sounds imingin on'both lines 10 and 11 to determine just what clicks heard were the clicks` indicating a switching of thei speech from one line to another. f-

Station 13 comprises apparatus similar to that already described' for station 12.`

Switching means synchronized -by apparatus notshown,"withfthe switching means of station 12 are, provided for-connecting contacts 65, 66, 67 and 68 in such a manner that a receiver 69 is responsive to currents in line section 10 when the signals from thetransmitter 14 are impressed thereon and isA redirection. llthe transmitter 7 0 by the switch:

ing apparatus will be alternatelyconnected to line sections 10 and' 11 and the switching ap aratus of station 12 operating in sync ronism therewith, will make the receiver at 14 responsive alwaysto that line on which the signaling currents happen to be. f

The system illustrated in Figure 3 somewhat similar to thatof Figure 1 except that the switching from one line section to `the other is obtained through the intermediation of vacuum tubes. and 81 are two vacuumtube repeaters connected in the socalled push-pull relation. The input circuit of tube 80 includes the secondary windingof a transformer 82, a battery 83 and a resistance 84; and the input circuit of tube 81 includes the secondary winding of the transformer85 and a resistance 86. /The cathodes of tubes 80 and 81 by a lead 102 are connected between resistance 84 and 86. The primaries of transformers 82 and 85 are associated with the telephone transmitter 87. Resistances 84 and 86 are adapted to be connected in series with a battery 88 when a perforation in tape `89 allows pin l90 to contact with block 91. Battery 88 of course, is not in circuit with the resistances 84 and 86 when perforations are not passing between contacts 90 and 91.

The batteries 83 and 88 should have such relative values that when the connections,

malV space current will flow through tube 81` as long as the connections forl battery 88` are broken. 'Vhen however, the connections for battery 88 are made it will be seen that the drop in potential across the terminals of resistance 86 can be made suchl that the grid of tube 81 will be made so negative asmade between contacts 90 and 91, while tubeA 81 is inoperative in this condition; and tube 81 will be operative and tube 80' inoperative whenever the connection between contacts 90 and 91 is broken.

The output circuit of tube 80 by transformer is `connected to the mid points of the line windings of a three winding transformer 96 so that when tube 80 isoperative currents from transmitter 87 will be amplified by tube 80 and impressed on line 97.

Similarly, the output circuit of tube 81 by a transformer 98 is connected to the mid points of the line windings of a three limbed `transformer 99 so that when tube 81 is operative amplified currents from transmitter 87.

Aare amplified by tube 81 and impressed by transformer 98 upon the line 100. It follows, therefore, as the tape 89 is pulled between contacts 90 and 91 that the signals from transmitter 87 will be switched from line section 97 `to line section 100 and vice.

'versa in accordance with any coderepresented by the arrangement of the slots in tape 89. 1

In order to 'connect the source of noise currents 101 to that line at any particular instant not employed in the transmission of signals from transmitter 87, two other vacuum tubes 103 and 104 are provided, which are connected in the so-called push-pull relation. The input circuit of tube 103 includes the secondary winding of a transformer 105 and also by lead 106 includes battery 83 and resistance 84. The input circuit of -tube -104 includes 'the secondary winding of transformer' 108 and by lead'109 also includes resistance 86. Since tube 103 contains in its input circuit battery 83 and resistance 84, it follows that tube 103 is operativewhen tube 80 is operative and is inoperative when tube 80 is inoperative. The output circuitof tube 103 by a transformer 110 is therefore connected to the mid oints of the three limbed transformer 99. t the time tube 80 is impressing the signal currents upon line section 97, tube 103 is impressing on line section the noise currents from source 101. r

Since tube 104 also includes in its input circuit resistance-86, it-follows that tube 104 81. The output circuit of tubflob a transformer 107 is therefore connec 1u`t0 the mid points of the line windingfsbi transformer 96 so thatitubey i304willserveto impress the noise'cprrents upon line 'section 97 at the time tnhejl' is impressing the true signaling currentsu on]line100.

Y- If desired the strength of the noise currents from source 101 may be varied, as in Fig. 1; in accordance with the strength of the signals from transmitter 87. Block 73 is intended to represent tubes and associated apparatus similar .to tubes 51, 56, etc.,

`109 and 110 connected in'the of 1.' Transformer 74 'would then correspond-*to transformer 50 of Flg. 1.

" The receiving apparatus for receiving sig- 'the secondary winding of a transformer 111 and also includes a resistance 112 and a battery 113. The input circuit of tube 110 includes the secondary winding of a transformer 114 and a resistance 115. The primary ,winding-of transformer 111 is in circuit with the third winding of the three limb transformer 117, while the rimary windin of transformerl 114 is in circuitwith the t 'rd winding of the three limb transformer 118.

Resistances v112 and 115 are adapted to be connected in circuit with battery 120 when the perforationsin tape 121 allow contact to bemade between contacts 122 and 123. By suitable mechanism, tape 121 is driven in synchronism with tape 89 and-if the forations in the ta es are similar, it follows that tube 109 will be operative when tube 80 is operative and tube 110 will be operative when tube 81 is operative. Tube 109 which by a connection previously traced is adapted to receive currents from line 97, will be operativeto receivev these currents at, the time when tube 80 is operative to impress currents online 97 from sourcey 87. Simi- 'larly tube 110 will be operative to receive currents from line 100 when tube 81is oper-v ative to impress currents from transmitter 87 upon line 100. Since the receiver 124 by transformers 125, and 126 is responsive to 'variations in the currents of the output circuits of both tubes -109 and 110, 'it follows that` receiver 124 will receive a faithful copy of signal current from transmitter 87.

The apparatus described above serves to transmit signals from 'transmitter 87! by lines -97 and 100 to the receiver 124. It 1s evident that transmitting apparatus similar to that associated with transmitter 87 may be located at .the station where receiver 124' is located for transmitting signals in the. opposite direction from that above de-A scribed. Block 135 is intended to represent the transmitting apparatus of this invention connected to the mid points of the line `Windings of the transformers 117 and 1158 lfor impressing the signals upon lines 97 and 100.v Suitable receiving apparatus. for these vsignals may be provided at block 136. Blocks 137 and 138 represent suitable artificial lines for Vbalancing line 100 whereby signals from vtransmitter 87 are not .impressed on the local receiving apparatus and whereby signals from source 135 'are not 'received by receiver 124. Blocksj139 and 140 represent` similar artiiicial lines for line 27. i

It is Vevident of course, thatthe receiver 1-24wil1 not receive the 'noise currents from source 101,since at the time noise currents percurrents impressed on the output lcircuit of v tube 130 cannot find their Way back by any connection whatsoever to the receiver 69;'

It is to be understood thatthe arrangement above described may be variously mod- 4-iiied Without departing in any way from the spirit of this invention asldefined in the appended claims. For example, this inventionv is not limited to the employment of only two channels between the transmitting station and the receiving station, since the invention broadly consists in transmitting portions of the signal overa plurality of channels or-by a plurality of carriers, successively or in any arbitrary order desired.

What is claimed is:

1. The method of signaling in which a plurality of si aling paths are employed to transmit'signa s in one direction, which comprises automatically switching at short intervals the lsignaling source from 011e of said paths to another and similarly switching a source of noise to a path that at any particular instant is not employed in the transmission of said signals.

2. The method of signaling in which two signaling paths are employed to transmit signals in one direction, which comprises automatically switchingthe signaling source from one path to the other alternately in accordance with a code, and simultaneously' switching a source of noise to that ath at any .particular-instant not employe in the transmission` of the signals.

3. A signaling system comprising a plurality .of channels, signal transmitting apparatus, signal receiving apparatus, means forlsimliltaneously lswitchin tervals said transmitting an receiving apparatus from one of said channels to another, .to enable signals to be transmitted from said transmitting apparatus to said reat short inwaves over one ,o said channels which at Lthe time is disconnected from' said transmitting and receivin apparatus.

4. The metho of signaling `in which a plurality of signaling paths are employed to transmit signals from a signaling source,

which comprises'switching at short intervals the signaling source from onejof said paths to another,'simultaneously switching a source of noiseto a line at any particular instant not employed in the transmission of said signals, and varying the intensity of said noise in accordance with the intensitly of said signals. 5. n a signaling system having transmitting and receiving stations, a plurality of transmission channels betw'een. said stations, a source of signal waves at said transmitting station, a signal receiver at said receivingstation, means for operatably associating said source of waves with' said transmission channels singly and in succession at pre-determined intervals, means for simultaneously shifting the said receiver, at the same intervals into operative association with the said channels whereby the receiver is associated during each interval with the same channel as said source of waves, and means coordinated with the means for shifting the associations of said source of waves and said receiver with said channels for sending other waves unrelated to said signal waves over one of saidchannels which is at the time out of operative associationwith said source of waves and receiver. i

6. rlhe method of signaling, -in which a plurality of carriers are employed between stations, which comprises automatically transferring the signals Jfrom one channel to another at irregular intervals, and similarly transferring noise currents from one channel to another at irregular intervals in such a manner that the signaling and noise currents at any particular instant are car audio ried by diiferent channels.

7. Themethod of signaling' employing a pluralityof carriers between stations, which comprises transferring the signals from one channel to another at irregular intervals, tranferring non-signaling'currents from one channel to another in such a manner that the signaling and non-signaling currents at any particular 'instant are 'carried by different channels, and controlling the intensiiy of the non-signaling currents in .accor ance with the intensity of the signals.

8. A signaling system comprising a line, a source of audio frequency signals of varying intensity, a source of audio frequency noise currents, and means for impressing on said line currents from said source of noise varyin in intensity in accordance with the equency signals.

9. A receiving system comprising an incoming line, two repeaters each havin input and output circuits, each of sai input circuits having portions in common and other portions individual to each repeater, and means for connecting an individual portion of each input circuit to said incoming line, and means for rendering said repeaters alternately operative lto repeat signalsy from said line.

10. 'In combination, two incoming lines, means for alternately applying two currents of different character to each of said lines, current of only one character to one line at a tlme, and a receiving system comprising two repeaters each -having an input circuit and an output circuit, eachfof said circuits having Vportions common to both repeaters and portionsl individual to. each vrepeater, means yfor connecting an individual portion o f each input circuit to a diierent one of sald incoming lines, and means asso- -ciated with the individualportions of the l2. In combination, two repeatersy each 4 having input and output circuits, said input circuits having certain portions in common and certain portions individual to each repeater, means for impressing signals on the individual portion of one input circuit, means for impressing signals on the individual portion of the otherl input circuit,

and means for alternately rendering said repeaters inoperative.

13. In combinationLtwo repeaters each having input and output circuits, Said input' circuits having certain portions in common and certain portions individual to each' repeater, means for impressing signals on the individual portion of one input circuit, means for impressing signals on the individual portion of the other input circuit,

'one-of said repeaters being normally inoperative, and means for rendering said last mentioned'repeater operative at times.

14. In an electric system, two repeaters each having input and output circuits, said' in ut circuits having certain portions indivi ual and other portions common to each repeater, two signal lines, a balancing network for each of said lines, a transformer having one winding` in circuit with one of said balancing networks, a second winding infcircuit with the corresponding line, and a third winding, a similar three winding transformer for said other line, connections between the individual portion of one of said input circuits and one of said thirdV windings, and connections between the individual portion of the other input circuit and said other third winding.

15. In an electric system, two repeaters each having input and output circuits, each of Isaid input circuits having portions in common and other portions individual to each repeater, a source of signals, means for operative. A* Y 16. In' an electric system, a plurahty of vacuum tubes, each having an anode, a cathode, and a control electrode, a source of voltage, a resistance, a connection between one of said anodes and its correspondin cathode comprising lsaid source and sai resistance, a condenser of low impedance to currents of speech frequencies in shunt to said resistance, connections whereby the drop in potential 'across the terminals of i said resistance is impressed between the conveo . reventing currents of trol electrode and the cathode of a second vacuum tube, a sourceof variable currents,

land means for impressin said currents between the control electro e and the cathode of said second vacuum tube- 17. In combination a vacuum tube'havi ing an output circuit, an impedance in said output 'circuit 4whereby, .a drop ofpotential across the terminals of said impedance is produced by the space current of said tube, a second vacuum tube having input terminals and an output circuit, said impedance being 'connected between' said input terminals, said resistance having such a value that the normaldirect current iiowing through said impedance produces a potential difference between said input terminals suiiicient to reduce substantially to zero the output current of' said second tube.

18. In combination a vacuum tube having an input circuit; and an output circuit,.

means for supplying signals of speech frequencies to said input circuit, a resistance in said output circuit, a receiving device, connectionsfrom said resistance to said receiving device, and means for substantially eech frequencies rom assmg through said resistance.

19. he method of producingl a direct current corresponding to the intensity of voice currents which'comprises rectitying said currents and filtering out the voice frequencies in' the rectified currents.

20. In a secrecy system, a signaling channel, a source of signaling currents, a source of non-signaling currents containing frequencies present inV andess'ential to said slgnaling currents, means for applying currents from said sources alternately to said channel, and means at the receivin end of said channel for separating said signaling currentsA from. said noirsignaling` currents.

21. In a secrecy' system, a signaling channel, a source of signaling currents, a source 'of non-signaling currents containing frequencies present in and essential tosaicl signaling currents, means for applying currents from said sources alternately to said channel, and means at the receiving end of said channel operatingsynchronously with said first recited means for separating said signaling currents from said non-s1gnaling currents.

22. In Aa secrecyv system, a plurality of signaling channels, a source of signaling currents, a source of non-signaling currents containing Afrequencies present in and essential' to said signaling currents, neans for vapplying currents from said sources alternately to each of said channels, and means at Vthe receiving ends of said channels for separating said signaling currents from said non-signaling currents and for combining the portions of said signaling currents received from said channels.

23. In a secrecy system, a plurality of signaling channels, a source of signaling currents, .a source of non-signaling currents containing frequenciespresent in and essential to said signaling' currents, means for applying currents from said sources alternately to each of said channels, and means at the receiving Aends of said channels operating 'synchronously with said lirst recited means for separating said signaling currents from said non-signaling currents and for combining the portions ofA said signaling currents received from said channels.

V24. In a transmission system, the combination with a source of waves to be repeated, of a transmission path including a space `dischar e device having a grid, means for controlling the Vtransmission characteristics e of said device for waves from said source comprising a source of control waves of vaxt'ying amplitude, a rectifier for rectiying sai Waves of varying amplitude to produce a varying direct current voltage, andmeans 'to utilize said voltage for polarizing the grid of said discharge device.

`25. In a transmission system, a space discharge device having a grid, a source of waves connected to the grid of said device to be repeated by said device and a control system 'for said discharge device comprising a source of waves of varying amplitude, a rectifier for rectifying,said waves to produce a direct current of varying magnitude, a resistance connected in the path of said direct-current, and a tap from said resistance to the grid of said device.

26., The method of rendering signals unintelligible which comprises impressing noise currents on a signaling channel and varying the amplitude of said noise currents in response to variations in the amplitude oi the signal currents.

27. The method'of-controlling an ampli- Iier which comprises rectify-,Ying speech curlll momes rents and varying the transmission eiciency er said amplier in accordance with lthe Variations orP the rectified currents.

28. The method of changing the ampiication of en ampliier having a control eiectrode which comprises rectifying speech currents and varying the potential of said controi eiectrode in accordance withV the variations of the rectied currents.y

En Witness whereof, hereunto subscrioe 'my naine this' 29th day of December B.,

.RALPH V. L Hemmer.

@ertifcate of Correction,

it is hereby certified that in Letters Patent No. 1,606,763, granted Not/einher 16, .1926, upon the application of-Ralph V. L. Hartley, of East Grange, New Jersey, for an improvement in Signaling Methods andfSystems, an. error appears 1n the printed specification requiring correctionas follower Page 2, 11ne 66, orf tube 5 1. read tube-56," and that the said Letters Patent should ybe reed with this correctlon therein that the same may conform to the recordpf the case inthe Patent Gce.

Signed and sealed this 21st dayof December, A. D.1v926.' I

[SEAL] i' i M. J. MOORE,

Acting aofmmz'ssz'oner of Patents. 

